1. Field of the Invention
The present general inventive concept relates to a method and apparatus to control a disk drive apparatus, and more particularly, to a method of calibrating parameters to measure the back electromotive force (BEMF) of a voice coil motor (VCM), and a method and apparatus to use the calibration method to perform unloading control.
2. Description of the Related Art
The present general inventive concept is related to inventions disclosed in U.S. Patent Publication Nos. 2002-054451 and 2002-149873, which are hereby incorporated herein by reference.
In U.S. Patent Publication No. 2002-054451, a method of measuring the BEMF of a voice coil motor in a disk drive, and a technology that uses this method to control the velocity of the VCM without a servo signal are disclosed. In U.S. Patent Publication No. 2002-149873, a technology that detects a value of a current flowing to a VCM to measure the BEMF thereof is disclosed.
In a disk drive, the velocity of a head must be precisely known in order to accurately control seeking and other operations. Conventionally, the velocity of the head is calculated using servo data written on the surface of the disk. The servo data includes track and sector numbers, which are used to calculate the velocity of the head.
However, these methods can be applied only when the head is able to read the servo data. For example, in ramp loading/unloading-type hard disk drives, the head is not disposed on the surface of the disk while the head is being loaded from the ramp to the disk or being unloaded from the disk to the ramp, so that the head cannot read servo data written on the surface of the disk. Therefore, the velocity of the head cannot be determined.
To solve this problem, in ramp loading/unloading-type hard disk drives, there is used a method of detecting the velocity of a head through the BEMF of the VCM driving the head slider, instead of using servo data.
Recently, in non-ramp loading/unloading-type hard disk drives, there has been adopted the same method of detecting the velocity of the head through the BEMF of the VCM, wherein the detected head velocity is fed back to control the velocity of the head in loading and unloading operations. Also, in a seek operation of the servo drive, the moving velocity of the head is detected through the BEMF of the VCM to control the moving velocity of the head in accelerating and decelerating regions.
However, when a current is applied to the voice coil motor (VCM) that moves the actuator of the disk drive, the temperature of the coil of the VCM rises. As the temperature of the coil rises, a change in the resistance value of the VCM occurs, thereby causing a change in the measured BEMF of the VCM by the amount of resistance value change. This applies especially to disk drives for mobile devices, which have thinner VCM coils, so that the change in resistance values of the coils through the current is comparatively larger. Therefore, the parameter values to measure the BEMF calibrated during loading cannot be used during unloading.
Likewise, a change in the resistance value of a VCM coil leads to errors in BEMF values, so that when the BEMF values are detected to control the head moving velocity, the head cannot be precisely controlled to move at a target velocity.